130 million years ago, there were two main landmasses. In the North, there was Laurasia, roughly corresponding to modern Eurasia and North America. In the South was Gondwana, corresponding to modern Australia, Africa, Antarctica, South America and the Indian subcontinent.

There was an intermittent land-bridge between Laurasia and Gondwana, between the modern North and South American continents, and at various times some contact between Africa and Europe.

Marsupials migrated via Europe into North America, and then to South America. By 100 million years ago, Africa had separated from the rest of Gondwana, and it does not seem that marsupials ever established themselves in Africa. They did, however, migrate into Antarctica and Australia.

The Laurasian marsupials all became extinct. Gondwana continued to break up, with Australia and then South America separating from Antarctica, and the landbridge between the Americas was also severed. Antarctica moved further south, the polar current was established, and it became much colder, and the marsupials went extinct in Antarctica. The formation of a stable isthmus between the Americas some three million years ago allowed marsupials to spread back into North America.

dv said:

130 million years ago, there were two main landmasses. In the North, there was Laurasia, roughly corresponding to modern Eurasia and North America. In the South was Gondwana, corresponding to modern Australia, Africa, Antarctica, South America and the Indian subcontinent.

There was an intermittent land-bridge between Laurasia and Gondwana, between the modern North and South American continents, and at various times some contact between Africa and Europe.

Marsupials migrated via Europe into North America, and then to South America. By 100 million years ago, Africa had separated from the rest of Gondwana, and it does not seem that marsupials ever established themselves in Africa. They did, however, migrate into Antarctica and Australia.

The Laurasian marsupials all became extinct. Gondwana continued to break up, with Australia and then South America separating from Antarctica, and the landbridge between the Americas was also severed. Antarctica moved further south, the polar current was established, and it became much colder, and the marsupials went extinct in Antarctica. The formation of a stable isthmus between the Americas some three million years ago allowed marsupials to spread back into North America.

Thanks.. I knew the rest but it was news that Europe was around back then..

Tell me more about Laurasion marsupials.

*a

Fair to say that when I say “Europe”, I mean that area of Laurasia roughly corresponding to modern Europe, and so on.

What can we deduce about the reproduction of the LCA of monotremes, marsupials and placentals?

dv said:

Fair to say that when I say “Europe”, I mean that area of Laurasia roughly corresponding to modern Europe, and so on.

I was only joshing.. ;)

LCA for eutherians and marsupials would have been in the late Jurassic, 150 to 130 mya, hard to be more precise than that.

LCS for monotremes and therians is taken to be Triassic, 250 to 200 mya. Fossil record of early monotremes is pissweak, but.

Yes but how did they reproduce?

OCDC said:

What can we deduce about the reproduction of the LCA of monotremes, marsupials and placentals?

Logic Cell Array?

Ah, how did who reproduce?

dv said:

LCS for monotremes and therians is taken to be Triassic, 250 to 200 mya. Fossil record of early monotremes is pissweak, but.

This one.

dv said:

Ah, how did who reproduce?

the Logic Cell Array

OCDC said:

dv said:

LCS for monotremes and therians is taken to be Triassic, 250 to 200 mya. Fossil record of early monotremes is pissweak, but.

This one.

Monotremes aren’t marsupial.

Oh, I see what you mean.

The non-egg-laying reproduction of the Theria is usually described as being “derived” while the egg-laying reproduction of the monotremes is described as “ancestral”. The earliest mammals were also probably egg layers.

so, it seems likely that the LCA of modern monotremes, marsupials and eutherians was a layer.

roughbarked said:

OCDC said:

dv said:

LCS for monotremes and therians is taken to be Triassic, 250 to 200 mya. Fossil record of early monotremes is pissweak, but.

This one.

Monotremes aren’t marsupial.

We know.

OCDC said:

roughbarked said:

OCDC said:

This one.

Monotremes aren’t marsupial.

We know.

It is OK, I’m not a docktar. ;)

dv said:

Oh, I see what you mean.

The non-egg-laying reproduction of the Theria is usually described as being “derived” while the egg-laying reproduction of the monotremes is described as “ancestral”. The earliest mammals were also probably egg layers.

so, it seems likely that the LCA of modern monotremes, marsupials and eutherians was a layer.

Ta. Do we have any fossilised mammalian eggs from then?

OCDC said:

dv said:

Oh, I see what you mean.

The non-egg-laying reproduction of the Theria is usually described as being “derived” while the egg-laying reproduction of the monotremes is described as “ancestral”. The earliest mammals were also probably egg layers.

so, it seems likely that the LCA of modern monotremes, marsupials and eutherians was a layer.

Ta. Do we have any fossilised mammalian eggs from then?

I’d imagine they’d be rare.

The Monotreme fossil record is scant and dates back to the Cretaceous.

Ta. Do we have any fossilised mammalian eggs from then?
-

No

Then go and find some!

dv said:

Ta. Do we have any fossilised mammalian eggs from then?
-

No

I’m told that: The marsupial fossil record dates back to the Mid-Cretaceous of North America.

So what evidence is that of Europe being where Laurasia was?

OCDC said:

Then go and find some!

If we can find the Laurasian Europe .. Cretaceous outcrops.

roughbarked said:

OCDC said:

Then go and find some!

If we can find the Laurasian Europe .. Cretaceous outcrops.

I’d like Doktars of palentology type, along when I’m digging opalised Cretaceous fossils.

I’m told that: The marsupial fossil record dates back to the Mid-Cretaceous of North America

—-

Earlier marsupial fossils are known from Asia and Europe
eg
http://news.nationalgeographic.com/news/2003/12/1215_031215_oldestmarsupial.html
http://www.sciencedaily.com/releases/2009/11/091106103510.htm

dv said:

I’m told that: The marsupial fossil record dates back to the Mid-Cretaceous of North America

—-

Earlier marsupial fossils are known from Asia and Europe
eg
http://news.nationalgeographic.com/news/2003/12/1215_031215_oldestmarsupial.html
http://www.sciencedaily.com/releases/2009/11/091106103510.htm

Thanks.. we do have an opalised platypus jawbone.. though I’m unsure of what date they put on that.. Haven’t seen a wallaby yet though. In Australia at the time there was probably too much water about.

Think I remember that being threaded at the time.

OCDC said:

Think I remember that being threaded at the time.

In the Cretaceous?

“…mammalian eggs…”

I came in late.

Is it possible for a creature which lays eggs to be a mammal, or for a mammal to lay eggs?

I thought that bearing live young was part of the definition of ‘mammal’.

captain_spalding said:

“…mammalian eggs…”

I came in late.

Is it possible for a creature which lays eggs to be a mammal, or for a mammal to lay eggs?

I thought that bearing live young was part of the definition of ‘mammal’.

Platypus and echidna.

I thought that bearing live young was part of the definition of ‘mammal’.

—

Well … you thought wrong.

captain_spalding said:

“…mammalian eggs…”

I came in late.

Is it possible for a creature which lays eggs to be a mammal, or for a mammal to lay eggs?

I thought that bearing live young was part of the definition of ‘mammal’.

Monotremes are mammals that lay eggs.
Living mammals are divided into egg-laying mammals, pouched mammals, and placental mammals.

roughbarked said:

Monotremes are mammals that lay eggs.
Living mammals are divided into egg-laying mammals, pouched mammals, and placental mammals.

Right. I knew about monotremes. Had the idea that they were a class of their own i.e. not mammals, but also not…?

captain_spalding said:

roughbarked said:

Monotremes are mammals that lay eggs.
Living mammals are divided into egg-laying mammals, pouched mammals, and placental mammals.

Right. I knew about monotremes. Had the idea that they were a class of their own i.e. not mammals, but also not…?

So you stopped reading about it back in 1800?

roughbarked said:

captain_spalding said:

roughbarked said:

Monotremes are mammals that lay eggs.
Living mammals are divided into egg-laying mammals, pouched mammals, and placental mammals.

Right. I knew about monotremes. Had the idea that they were a class of their own i.e. not mammals, but also not…?

So you stopped reading about it back in 1800?

sorry, I was trying to be funny.. It probably didn’t work.. I need to remember when to put the filters on.

roughbarked said:

captain_spalding said:

roughbarked said:

Monotremes are mammals that lay eggs.
Living mammals are divided into egg-laying mammals, pouched mammals, and placental mammals.

Right. I knew about monotremes. Had the idea that they were a class of their own i.e. not mammals, but also not…?

So you stopped reading about it back in 1800?

Well, that was only about two hours ago.

No, things just get a bit fuzzy when it’s like half a century since your last biology class,

captain_spalding said:

roughbarked said:

captain_spalding said:

Right. I knew about monotremes. Had the idea that they were a class of their own i.e. not mammals, but also not…?

So you stopped reading about it back in 1800?

Well, that was only about two hours ago.

No, things just get a bit fuzzy when it’s like half a century since your last biology class,

You aren’t the lone stranger there.

Three types of mammals: – placental eg hew-mon – foetus develops inside mother, then feeds on milk after birth but – marsupial eg koala, possum – foetus develops for a much shorter period in the mother then latches on to a nipple in the pouch for yonks after birth – monotremes ie platypus, echidna – lay eggs, make milk but without distinct nipples

Stupid formatting.

Three types of mammals:
1) placental eg hew-mon – foetus develops inside mother, then feeds on milk after birth but
2) marsupial eg koala, possum – foetus develops for a much shorter period in the mother then latches on to a nipple in the pouch for yonks after birth
3) monotremes ie platypus, echidna – lay eggs, make milk but without distinct nipples

LCA = Latest Common Ancestor?
LCS = ?????

>130 million years ago, there were two main landmasses. In the North, there was Laurasia, roughly corresponding to modern Eurasia and North America. In the South was Gondwana, corresponding to modern Australia, Africa, Antarctica, South America and the Indian subcontinent.

Well I’m sure that is one take on it. I suspect that PWM will be along shortly to give the alternative, and obviously more correct, interpretation.

places pinky next to outer lips

http://www.youtube.com/watch?v=mXD7YOoHpAs

The other way of looking at it is that there are two types of mammals: monotremes and therians.

There are also two types of therian: placentals and marsupials.

dv said:

The other way of looking at it is that there are two types of mammals: monotremes and therians.

There are also two types of therian: placentals and marsupials.

simplification amidst multiplication..

simplification amidst multiplication..

—-

It is not a completely petty point, though. The marsupials and placentals are considered much more close than (marsupials and placentals) are to monotremes.

dv said:

simplification amidst multiplication..

—-

It is not a completely petty point, though. The marsupials and placentals are considered much more close than (marsupials and placentals) are to monotremes.

I didn’t think my comment was petty but if you do then so be it.. ;)

I didn’t think my comment was petty but if you do then so be it.. ;)
—-

I didn’t think your point was petty at all. I was referring to my own point.

dv said:

I didn’t think my comment was petty but if you do then so be it.. ;)
—-

I didn’t think your point was petty at all. I was referring to my own point.

no fuss at all then.. ;)

The monito del monte is the only extant member of its family (Microbiotheriidae) and the only surviving member of an ancient order, the Microbiotheria. The oldest microbiothere currently recognised is Khasia cordillerensis, based on fossil teeth from Early Palaeocene deposits at Tiupampa, Bolivia. Numerous genera are known from various Palaeogene and Neogene fossil sites in South America. A number of possible microbiotheres, again represented by isolated teeth, have also been recovered from the Middle Eocene La Meseta Formation of Seymour Island, Western Antarctica. Finally, several undescribed microbiotheres have been reported from the Early Eocene Tingamarra Local Fauna in Northeastern Australia; if this is indeed the case, then these Australian fossils have important implications for understanding marsupial evolution and biogeography.

In common with reptiles and marsupials, monotremes lack the connective structure (corpus callosum) which in placental mammals is the primary communication route between the right and left brain hemispheres. The anterior commissure does provide an alternate communication route between the two hemispheres, though, and in monotremes and marsupials it carries all the commissural fibers arising from the neocortex, whereas in placental mammals the anterior commissure carries only some of these fibers.

OCDC said:

if this is indeed the case, then these Australian fossils have important implications for understanding marsupial evolution and biogeography.

but this is why doktars are doktars.. we rely upon their findings.

The sequencing of the platypus genome has also provided insight into the evolution of a number of monotreme traits, such as venom and electroreception, as well as showing some new unique features, such as the fact that monotremes possess 10 sex chromosomes and that their X chromosome resembles the sex chromosome of birds, suggesting that the two sex chromosomes of marsupial and placental mammals evolved more recently than the split from the monotreme lineage.

OCDC said:

The sequencing of the platypus genome has also provided insight into the evolution of a number of monotreme traits, such as venom and electroreception, as well as showing some new unique features, such as the fact that monotremes possess 10 sex chromosomes and that their X chromosome resembles the sex chromosome of birds, suggesting that the two sex chromosomes of marsupial and placental mammals evolved more recently than the split from the monotreme lineage.

Which, apart from the other details.. also makes them unique.

All of the Laurasian marsupials so far found have been small. Mouse sized.

dv said:

All of the Laurasian marsupials so far found have been small. Mouse sized.

not surprising.. all mammals were at the time.

Yes …

Seems to be that when they got to South America, they more or less ran the joint, filled niches like a motherfucker.

dv said:

Yes …

Seems to be that when they got to South America, they more or less ran the joint, filled niches like a motherfucker.

I have a joke about those I’ll take to chat..

Dromiciops gliroides is a sweet looking fellow.